In an experiment, the bird and his owner were put in separate rooms and filmed as the artist opened random envelopes containing picture cards.

Analysis showed the parrot had used appropriate keywords three times more often than would be likely by chance.

Captives' frustrations

This was despite the researchers discounting responses like "What ya doing on the phone?" when N'kisi saw a card of a man with a telephone, and "Can I give you a hug?" with one of a couple embracing.

Professor Donald Broom, of the University of Cambridge's School of Veterinary Medicine, said: "The more we look at the cognitive abilities of animals, the more advanced they appear, and the biggest leap of all has been with parrots."

Alison Hales, of the World Parrot Trust, told BBC News Online: "N'kisi's amazing vocabulary and sense of humour should make everyone who has a pet parrot consider whether they are meeting its needs.

"They may not be able to ask directly, but parrots are long-lived, and a bit of research now could mean an improved quality of life for years."